This invention relates to telephone systems over which data traffic may pass, and in particular, to those systems which permit communications with a data process.
For the transfer of data through telephone systems, it is well known in the art to provide data devices at the subscriber stations. These data devices are connected to the communication line by means of special alternating switches, and they enable data transmission over the telephone communication path. As a rule, these terminal units are very costly and complex and in many cases not needed at all. For example, the aforementioned data devices are not needed, if a central data processor can be dialed from various subscriber stations to obtain specific automatic announcements, such as statements of account, stock quotations, inventories, etc. or to execute orders. In these cases, the telephone itself can be employed as a terminal unit. Using the telephone instrument the data input is effected by means of the dialing system, while the data output occurs acoustically through the data processor in the form of sound or speech, and, thus, can be received over the telephone receiver.
A disadvantage in this type of data service having acoustic data output through the data processor is that in many cases a desired permanent recording of the conversation conducted with the data processor is lacking.
To overcome this deficiency a printer could additionally be provided in each subscriber set. The printer would be activated over a separate output unit and output line. This, however, would require a large amount of additional circuitry adding significantly to the cost and complexity of the system.